494 Dansk Botanisk Arkiv, Bd. 3. Nr. 1. 



migrate this distance is, of course, not impossible, but in order 

 to explain the great similarity between the West Indian and the 

 Indo-Pacific algal flora his explanation is not sufficient. It is well 

 known that, owing to geological reasons, the supposition has been 

 adopted that the Pacific Ocean and the Atlantic have been in 

 direct communication through Central America as late as in the 

 Tertiary Period. But if this is the case the algal floras of both 

 oceans have then had the opportunity of easy communication. 



Regarding the geographical distribution of the Caiilerpas, 

 SvEDELius^) has adopted this explanation as the most natural 

 one. In comparing the 21 species of Caulerpas found by him at 

 the shores of Ceylon with those found in the West Indies, 

 SvEDELius discovered that no less than twelve (according to his 

 definition of species), were common to both areas. Svedelius 

 writes: "It is very remarkable that the tropical algal district in 

 the Atlantic is almost confined to the West Indies. This probably 

 depends on the eastern coast of South America, just as the western 

 coast of Africa — as Murray points out, not oflering suitable 

 habitats for algal growth. But then one can scarcely assume that, 

 even if warmer water washed the south coasts of South America 

 and especially of Africa, a more luxuriant algal vegetation should 

 have been harboured then than is the case to-day, seeing how 

 little suited they are said to be for algal growths of any kind. I 

 therefore think that the communication and the relationship 

 between the floral districts of the Indian-Pacific Ocean and the 

 West Indies can be more naturally explained in another way, 

 i. e., that these districts once had direct communication over 

 the districts where now the Central or South American continent 

 separates the two great oceans". 



Of the 11 species of Caulerpa found at the West Indian Is- 

 lands examined by me, 9 are also found in the Indo-Pacific Ocean, 

 and if it might be proved that Caulerpa ambigua Okamura is like 

 my Caulerpa Vickersiæ no less than 10 are common to both areas, 

 the Caulerpa Ashmeadi, being the only specific West Indian 

 species found, having a rather restricted distribution. And just 

 the fact that, which I have mentioned above, it is the Chloro- 

 phyceæ, and among them especially such old genera as Caulerpa^ 



1) Svedelius, N., Ecological and systematic Studies of the Ceylon Spe- 

 cies of Caulerpa (Ceylon Marine Biological Reports, Nr. 4). 



